1. Field of the Invention
This invention relates to a surfactant system useful in dishwashing machines, and more particularly to a surfactant system comprising a compatible mixture of at least one uncapped ethoxylated nonionic medium-to-high foaming surfactant and at least one propylene oxide capped nonionic low foaming surfactant. This surfactant system is useful in dishwashing detergents and as rinse aids which have a good wetting and drainage effect on hard surfaces.
2. Background Information
Many cleaning applications require surfactants that are both low foaming and defoaming. Examples include automatic dishwasher detergents, textile processing, paper processing, ore processing and metal cleaning. Here the typical ethoxylated nonionic surfatants must be subjected to a capping process to meet these requirements. Capping reactions with propylene oxide or other suitable chemicals are a costly extra step in the production of these surfactants.
In the art of cleaning compositions for use in cleaning hard surfaces, particularly the art of cleaning tableware and other food-soiled utensils in machine dishwashers, the problem of excessive foam buildup in the machine during operation is the result of high food soil concentrations. The use of alkyl phosphate ester defoamers such as monostearyl acid phosphate as disclosed in U.S. Pat. No. 3,314,891 has largely solved the problem of excessive foam buildup. Prior thereto, machine dishwashing compositions had a tendency to foam excessively and/or leave undesirable spots and streaks on dishes and glassware. The low foaming nonionic surfactants contained in such detergent compositions were ineffective in both removing food soil and providing suitable foam control where the aqueous cleaning solution became contaminated with foam generating protein soils such as egg soil and soil from various milk products.
The generation of such foams is particularly insidious in that the cleaning action of the machine dishwasher depends to a large extent upon the effective suppression of foam generation during operation. Without effective foam suppression, the mechanical cleaning action of the machine dishwasher is reduced as the result of foam buildup in the aqueous cleaning solution. The aqueous washing fluid which is normally impelled against the tableware in the machine dishwasher is less effective in cleaning because it is forced against the tableware at reduced pressure.
An indication of the various kinds of nonionic surfactants utilized in such machine dishwashing compositions can be found in U.S. Pat. Nos. 3,314,891 and 3,359,207. General disclosures of nonionic surfactants can be found in U.S. Pat. Nos. 2,677,600; 2,979,528 and 3,036,118. Low foaming washing and cleaning agents for use in machine dishwashing are also disclosed in U.S. Pat. No. 3,382,176. Machine dishwashing detergent compositions containing a nonphosphate salt builder have been disclosed in British Pat. No. 1,325,645; Canadian Pat. No. 941,707; U.S. Pat. Nos. 3,899,436; 4,127,496 and 4,092,258.
Another method of reducing the foaming tendency of ethoxylated alcohols was to end cap them with an alkyl group. For example, Henkel has a series of patents using capped surfactants to suppress foam. In the following, "EO" is an ethylene oxide residue, "PO" is a propylene oxide residue, "BO" is butylene oxide residue, and "AO" is an alkylene oxide residue. Henkel published patent application ZA 89/4027, 1990 discloses a low foam surfactant composition that produces little foam and good wetting on plastics (especially polycarbonates) and that are recommended for rinse aid applications in automatic dishwashers. The nonionic surfactants used therein included C.sub.8-18 --O--(EO).sub.x --C.sub.8-14 alone or in combination with one or more of C.sub.8-18 --O--(EO).sub.a --(PO).sub.b --H, C.sub.8-18 --O--(EO).sub.c --C.sub.4-8 and C.sub.8-18 --O--(EO).sub.d --H, where a=2 to 6, b=3 to 7, c=7 to 12, d=20 to 50 and x=20 to 40. This patent application also discloses the processes for their production. DE 3,928,604 discloses foam-inhibiting alkyl polyglycol ethers for detergents including C.sub.8-14 --O--(EO).sub.2-8 --C.sub.8-10 which can be used in mixtures with C.sub.8-18 (EO).sub.7-10 --H in ratios of 10:90 to 90:10. Suggested applications are for machine dishwashing detergents. DE 3,935,374 discloses a compound with good anti-foaming activity and is shown by C.sub.6-18 --O--(EO).sub.3-6 --C.sub.4-8. These are made with a narrow range molecular weight distribution ethoxylation catalyst. EP 254206 discloses low-foam/foam-depressing surfactant mixtures containing C.sub.8-18 --O--(EO).sub.3-7 --C.sub.4-8 and C.sub.8-18 --O--(EO).sub.1-3 --(PO).sub.3-66 --H optionally with C.sub.16-22 --O--(PO).sub.1-3 --H. Henkel patent (DE 4,009,533, 1991) discusses mixtures for laundry applications in the form of: alkyl glucose compounds with R--O--(EO).sub.0-15 --(AO).sub.1-20 --OR' with R=C.sub.8-22 and R'=C.sub.1-10.
Encolab Inc., U.S. Pat. No. 4,973,423, 1990 claims foam inhibiting additives or low-foam cleaners. The additives are the alkyl end-capped ethoxylated alcohols C.sub.6-18 --O--(EO).sub.2-6 --C.sub.4-8 used in conjunction with wetting agents such as nonionic surfactants, including polyglycol ethers of the type obtained by adding ethylene oxide onto alcohols.
Due to the additional processing steps and cost involved in alkyl end-capping, the search continued and still continues for low foaming and defoaming nonionic surfactants which avoid such steps and cost.
Drackett Co., U.S. Pat. No. 4,226,736, 1980 discloses mixtures of surfactants and thickeners to make gel type automatic dishwasher detergents. The surfactant mixtures consist of polypropoxylated polyethoxylated ethylene glycols and C.sub.10-18 --O--(EO/PO).sub.55-80% --H.
Nippon Paint Co., U.S. Pat. No. 4,256,601, 1981 discloses a low foam surfactant with very good foam breaking abilities which is the all para X--Ph--CR.sub.1 R.sub.2 --Ph--O(AO).sub.3-20 H. This material is mentioned in combination with nonionic substances that have a cloud point less than 40.degree. C. such as alcohol ethoxylates, alkylphenol ethoxylates and block copolymers of the (EO)--(PO)--(EO) type. The weight ratio of the above compound to the nonionics is given as a range of 1.0 to 0.05 up to 1.0 to 5.0.
Sandoz Ltd. patent (Abstracts of GB 2204321-B, 1991 and GB 2204321-A, 1988) discusses biodegradable detergent compositions for cleaning surfaces (metals, plastics, laundry) which in addition to an alkanolamine and sequestering agent include the mixture of a fatty alcohol polyethylene glycol ether and a low foaming nonionic surfactant as represented by: C.sub.8-22 --O--(EO).sub.5-25 H (2-35%) and C.sub.8-22 --O--(EO).sub.1-12 (PO).sub.1-5 H (0.5-5.0%), respectively. According to GB 2204321-A, 1988, the preferred mixture in the surfactant composition was C.sub.12-16 --O--(EO).sub.5-12 H and C.sub.14 --O--(EO).sub.5 --(PO).sub.4 H. In Example 2 thereof, laboratory glassware contaminated with dried blood, brain substance and albumin was immersed in a solution containing from 3 to 5% by weight of a composition containing 12% by weight C.sub.12/15 --O--(EO).sub.7 H and 1% by weight C.sub.12 --O--(EO).sub.5 --(PO).sub.4 --H for 2 to 3 hours at 80.degree. C. or 12 hours at room temperature. There was no mention of low foam nor defoaming with this combination. The remaining examples dealt with laundry detergents (continuous working process through wash tunnel) and cleaning electronic microcircuits (immersion) and watch cases (ultrasonic treatment).
Henkel published patent application WO 91/03536, 1991 discloses foam-inhibiting additives for low foaming cleansers. These additives are: C.sub.12-20 --O--(EO).sub.2-5 H where the alkyl group is from a 2-branched even alkanol and optionally mixed with C.sub.8-18 --O--(EO).sub.2-6 --(PO).sub.3-7 --H where the alkyl group can be branched or linear. The 2-branched aspect of the ethoxylated alcohol is stressed in part by seizing on the observation that slight structural changes produce significant differences in the properties of nonionic surfactants. For example, DE 3,315,951 and 3,800,493 were compared. The primary differences therebetween were the carbon residue of the alcohol used in each case. In the first, the carbon residue had 8 to 18 carbon atoms and that of the other had 20 to 28 carbon atoms. Surfactants with highly branched chains generally show lower foam heights than isomeric straight-chain materials, except where the length of the hydrophobic group becomes too long for straight-chain compounds to have adequate water solubility for good defoaming (e.g., greater than 16 carbon atoms at 40.degree. C.). See "Surfactants and Interfacial Phenomena" by Milton J. Rosen, p. 212, published by Wiley Interscience (1978). As exemplified in this Henkel patent, the branched portion of the alkyl group ranged from 4 to 8 carbon atoms with the straight portion of the alkyl group ranging from 8 to 12 carbon atoms. Accordingly, this Henkel patent teaches away from straight or unbranched alkyl groups in the ethoxylated alcohol so as to effect a reduction in its foaming tendencies.
Henkel published patent application ZA 90/10,356, 1991 discloses industrial cleaners mainly used for cleaning and passivating in spray-cleaning units in the automotive industry. The industrial cleaners use a combination of surfactants for cleaning hard surfaces and which exhibit low foaming properties from 15.degree. C. to 80.degree. C. and excellent wetting properties without leaving spots and stains. The surfactant combination contains
(a) C.sub.6-18 --O--(EO).sub.2-12 --H and PA1 (b) C.sub.6-18 --O--(EO).sub.2-10 --(PO).sub.2-8 --H PA1 (C) C.sub.6-18 --O--(EO).sub.2-12 --C--.sub.1-8. PA1 (a) at least one first nonionic surfactant having a general formula selected from the group consisting of general formula (I) EQU R.sup.1 --O--(CH.sub.2 CH.sub.2 O).sub.y --H (I) PA1 wherein R.sup.1 represents a linear alkyl or olefinic group having from about 6 to about 18 carbon atoms and y represents a number ranging from about 3 to about 15, and general formula (II) EQU Np--O--(CH.sub.2 CH.sub.2 O).sub.z --H (II) PA1 wherein Np is the carbon residue of nonylphenol or octylphenol and z represents a number ranging from about 4 to about 200; and PA1 (b) at least one second nonionic surfactant having a general formula selected from the group consisting of general formula (III) EQU R.sup.2 --O--(CH.sub.2 CH.sub.2 O).sub.m --A.sup.1 --H (III) PA1 wherein R.sup.2 represents a linear or branched alkyl or olefinic group having from about 6 to about 16 carbon atoms, m represents a number ranging from about 3 to about 15, and A.sup.1 represents a group having the formula --(CH.sub.2 --CH(CH.sub.3)--O).sub.q --, --(CH(CH.sub.3)--CH.sub.2 --O).sub.r -- or a combination thereof with q and r each representing a number ranging from 0 to about 30 and the sum of q and r represents a number ranging from about 4 to about 30, and general formula (IV) EQU R.sup.3 --O--A.sup.2 --(CH.sub.2 CH.sub.2 O).sub.n --A.sup.3 --H(IV) PA1 wherein R.sup.3 represents a linear or branched alkyl or olefinic group having from about 6 to about 18 carbon atoms, n represents a number ranging from about 10 to about 25, A.sup.2 represents a group having the formula --(CH.sub.2 --CH(CH.sub.3)--O).sub.t --, --(CH(CH.sub.3)--CH.sub.2 --O).sub.u -- or a combination thereof with t and u each representing a number ranging from 0 to about 15 and the sum of t and u represents a number ranging from about 2 to about 15, and A.sup.3 represents a group having the formula --(CH.sub.2 --CH(CH.sub.3)--O).sub.v --, --(CH(CH.sub.3)--CH.sub.2 --O).sub.w -- or a combination thereof with v and w each representing a number ranging from 0 to about 55 and the sum of v and w represents a number ranging from about 10 to about 55, PA1 wherein the components a and b above are compatible with each other. Components a and b are preferably present in a mole ratio a:b ranging from about 95:5 to about 60:40. PA1 (1) from about 0.1% to about 5%, preferably from about 0.1% to about 2.5% of a bleach-stable, compatible surfactant mixture of the present invention; PA1 (2) from about 5% to about 40%, preferably from about 15% to about 30% of a detergency builder, especially a builder selected from the group consisting of sodium tripolyphosphate, sodium carbonate, potassium pyrophosphate and mixtures thereof; PA1 (3) a hypochlorite bleach to yield available chlorine in an amount from about 0.3% to about 20.0%, preferably from about 0.5% to about 1.5%; PA1 (4) from about 0.1% to about 10%, preferably from about 0.5% to about 5% of a thickening agent, preferably a clay thickening agent or a cross-linked water insoluble polycarboxylate agent; PA1 (5) alkali metal silicate to provide from about 3% to about 15%, preferably from about 5% to about 12.5% of SiO.sub.2 ; PA1 (6) about 0.1 to about 0.5% of a physical stabilizer such as a fatty acid or soap; and PA1 (7) the balance an aqueous liquid.
where the weight ratio of (a):(b) is within the range of 10:1 to 1:10. The carbon residue of components (a) and (b) are preferably linear. The surfactant combination may further contain